1. Field of the Invention
This invention relates to containers, and more specifically, to containers made of synthetic plastics film material.
2. Description of the Prior Art
It is known to manufacture flexible containers in large quantity and at low cost from synthetic plastics film material and to provide such containers each with a closure comprising pressure sensitive contact adhesive for uniting one to another adjacent surfaces of an opening of the container. Generally, the closure is in the form of a flap which is united with an opposite facing surface of the container by means of the adhesive.
A convenient method of providing pressure sensitive contact adhesive to form closures for containers is to apply adhesive tape to material from which the containers are to be manufactured, the tape thereby being incorporated in the finally formed containers such that portions of the tape comprise the closure of the containers.
Such containers generally comprise front and rear panels united one to another in spaced substantially parallel seams, one of the panels having a line of separation extending substantially orthogonal to the seams and a tape applied by a pressure sensitive contact adhesive to the said one panel so as to extend longitudinally of and bridge the line, the adhesive being separable in relation to a surface in contact therewith.
In French Pat. No. 2,345,355 (Janowski), for example, there is proposed a method of manufacturing tamper evident containers of synthetic plastics film material in which the material is in the form of a web and is advanced through a machine in a direction parallel to a longitudinal axis of the web. The web is folded longitudinally, is slit longitudinally, is provided with an adhesive tape which extends longitudinally of and bridges the slit and the web subsequently is provided with spaced transversely extending rows of perforations. Finally, the web is slit and welded in spaced transverse welds providing spaced substantially parallel seams adjacent corresponding rows of perforations in completed containers thereby formed by the slitting and welding process. A portion of an adhesive coating of the tape provides closure means for the completed bags.
A serious disadvantage of the method proposed in French Pat. No. 2,345,355 is that, in order to carry out the method, it would be necessary to modify extensively existing machinery whereby such machinery would be provided with means for accurately providing the transversely extending rows of perforations.
A further disadvantage of containers manufactured in accordance with French Pat. No. 2,345,355 is that, although the spaced parallel rows of perforations define a flap which would be separated from adjacent portions and peeled away therefrom to open a container and thereby provide a tamper evident feature, the container would not be air tight when closed because air would pass freely into the interior of the container through the perforations. In consequence, the containers could not be used for packaging of items adversely affected by ingress of air.